DESCRIPTION: (provided by the applicant) The main objective of Project 8, Structure/Properties of Altered Forms of Dentin and Cementum, is to determine specific material "signatures" for key variations and alterations of dentin and cementum in both primary (deciduous) and permanent teeth. The material "signature" will be defined by characteristic microstructures, composition and selected properties (mechanical and demineralization) for each form or variation of dental hard tissue. We hypothesize that the "signatures" will provide a unique identifier for each alteration. These "signatures" should prove instrumental for developing improved clinical approaches to preventive and conservative, restorative dentistry. We will carry out this work in an ordered, repeated measures design involving a variety of advanced methods including x-ray tomographic microscopy (XTM), atomic force microscopy (AFM) for imaging, demineralization and nanoindentation measurements, small angle x-ray scattering (SAXS) and other standard tools, allowing determination of characteristics of mineral, and collagen fibril structure, repeat distances and cross-links. Aim 1 will define the "signature" for transparent dentin associated with coronal caries and attrition in primary and permanent dentin; sclerotic cervical lesions, endodontically treated teeth, and aging of the root. It will also evaluate the mineral level, structure and nanomechanical properties variations of the zones in active and arrested root caries, and identify unique characteristics of dentin associated with Dentinogenesis Imperfecta (DI-II). Aim 2 will focus on changes associated with collagen cross-link patterns and fibril structure for each variation. Aim 3 evaluates the "signature" of secondary and tertiary dentin in primary and permanent teeth, and evaluates the dependence of tertiary dentin "signature" on the nature of the stimulus. Aim 4 will determine the age-dependent key components of the "signature" i.e., structure and properties of cellular and acellular cementum, the cementun-dentin junction (CDJ), and the cementun-enamel junction (CEJ) using the same approach and generally the same teeth as those used for dentin. The "signatures" from this project will provide fundamental information that will be used to develop a model in Project II, understand the substrate for bonding in Project III and will serve as a baseline for comparison with the "signatures" of mouse teeth in Project IV.